This is a gross exaggeration. I can't think of any of their songs where they stole an exact melody from another song. All the songs I can think of that were "ripped off" were not even close to exact copies. Can you please give me examples of these exact melodies they stole?It's not that band has to be incredibly original. I like the Alkaline Trio, Pedro the Lion, and other bands that aren't amazingly original. But they still write really good songs. The reason I have no respect for Sum 41 is that they seem to lack the ability to write good songs, so they steal. I don't see it as being inspired by, because usually being inspired by means that you take a general theme, idea, or sound and incorporate it into something that you're doing. Not flat out take the exact melody from the song.
Also, sure, Sum 41 isn't exactly awesome at writing songs... but I think their original songs aren't terrible. They're just typical pop punk songs, but it's not like they take ideas because they can't write their own songs. In fact, on the album that had so much "theft", it was like 3 or 4 songs out of like 14 that had notions of stuff being stolen. So you're making sweeping claims again... 3 or 4 songs could easily be accidental, just as much as RHCP or Offspring. Ever try writing songs? I've written a few songs, and then realized months later that, no wonder that melody came so easy, it's from a song that's already been done. It's happened a good 2 or 3 times, and I've only written 12-15 songs total.